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The Keystone pipeline ... explained

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The Keystone pipeline ... explained01:47

Washington (CNN)Prospects for a bill approving the Keystone XL pipeline improved greatly on Wednesday after senators voted on a large batch of amendments to the controversial measure. The Senate is now likely to vote Thursday on passage of the legislation.

The amendment votes were designed to satisfy a group of nine Democratic supporters of the pipeline -- who are needed to give the bill the 60 votes required to clear the Senate -- after they were angered last week when Republicans, who control the chamber, abruptly tried to end debate on the bill.

In fact, the outcome of the votes on the amendments was less important than the fact that senators were allowed to vote on them at all.

"It is now time to get through the remaining amendments and vote up or down on passage of this bill before we leave for the week," said Senate Majority Leader Mitch McConnell on the floor on Wednesday. "We expect the filibuster of good American jobs to soon come to an end."

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Leadership aides in each party predicted that because of the additional amendments enough of those Democrats would now support the bill. However, aides to most of the individual senators contacted by CNN wouldn't confirm how their senators would eventually vote.

The Republican floor manager of the bill, Lisa Murkowski of Alaska, said "serious and significant negotiations" between her and her Democratic counterpart, Maria Cantwell of Washington, led to the agreement to vote on as many as 18 amendments on Wednesday.

Murkowski said by the time debate ends on Keystone there will have been about 50 votes on amendments. She called that number "pretty considerable" since in 2014 when the Democrats controlled the chamber "there were just 15 amendments considered in the entire year."

But a spokesman for Senate Minority Leader Harry Reid said the votes didn't come about because of GOP generosity, rather, Adam Jentleson argued, Republicans buckled to pressure from Democrats to allow additional votes.

"If Sen. McConnell had his way, none of these amendment votes would have happened," Jentleson said. "But we are glad Sen. McConnell reversed course and heeded Democrats' call for an open amendment process."

After more than four hours of voting, nearly all the amendments were defeated, unable to get over a 60-vote threshold senators agreed would be needed for passage.

They included a proposal from Sen. Ted. Cruz, R-Texas, to boost exports of liquefied natural gas; an amendment from Sen. Jerry Moran, R-Kansas, to delist the lesser prairie chicken as a threatened species; a campaign finance amendment from Sen. Sheldon Whitehouse, D-Rhode Island, and a proposal from Sen. Bernie Sanders, I-Vermont, dealing with rebates for solar power.

A key procedural vote is scheduled for Thursday. If enough Democrats end up voting for it, a vote on passage of the bill is likely later in the day, senators and aides said.

Regardless, President Barack Obama has promised to veto the bill, arguing the decision should be left up to the executive branch, and it appears pipeline supporters are short the 67 votes they would need to override it.